WAN Network Protocols - DSL, SONET, HDLC, DWDM, DLSW+

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This article describes the implementation of protocols in the WAN enterprise network environments today HDLC, DSL, SONET, DWDM and DLSw +

High level Data Link Control (HDLC)

HDLC is a Cisco proprietary protocol designed to send data over serial links. It defines an encapsulation method for data link layer for transporting data over a public or private network. This protocol is used toTDM leased line. TDM circuits are probably the oldest types of circuits from circuit switching technology developed by the Public Switched Telephone Network carries traffic that uses the phone. The difference is that companies need to carry data traffic speed model 256 Kbps to 45 Mbps is just a circuit that requires the data at the beginning and at the end, what a phone line for conditioning and formatting data for these speeds.

The TDM network is working withSteps called digital signal zero (DS-0). A DS-0 is a 64 kbps channel (56 kbps, when in-band signaling), is the part of the DS-1 specific industry standards. A DS-1 defines a standard for the design of transmission on a T1 circuit at 1.544 Mbps with 24 channels DS-0. A DS-3 standard defines a frame for transmission over a circuit T3 44.736 Mbps with 28 channels DS-1. Some service providers offer what is called fractional T1 (Frac T1). It 'a circuit that operates at a lower speed1,544 Mbps as well, as there is a subset group of 24 channels.

The common fractional T1 speeds of 384 Kbps, which is composed of six DS-0 channels. Many routers have a serial interface function, the shared channel or a T1 circuit. This is useful if you do not want to pay for a full T1 circuit. This is done by differentiating each specific channel full T1 circuit. Europe is called something other than standard circuit speed E1and E3. The E1 circuit is composed of 30 channels DS-0and operates at 2.048 Mbps, while E3 is made up of 20 T1 channels and operates at 34.368 Mbps.

Digital Subscriber Line (DSL)

Digital Subscriber Line is one of the latest broadband technologies that are used for remote access and dial-office. It 'very affordable when compared with ISDN and T1circuits, because it is faster and less expensive. The problem with DSL is that it should not be higher than 18,000 feet from the center service provider. The demand forHigh-speed Internet access service is the installation of DSL equipment on many key points. This increases the chances of availability in your area, if it is not an option today. The current specification defines three key technologies, asymmetric DSL (ADSL), Very High Data Rate DSL (VDSL) and symmetric DSL (SDSL) are.

Asymmetric DSL (ADSL), as the name implies, is the ADSL technology, which allows higher speeds downstream of theService provider for the customer to the upstream speed from client to service provider. The project corresponds to the flow of Internet and video applications, because usually the customer to download more information and will not send them. Depending on the distance from the service provider's central downstream speeds can be faster than 6 Mbps and upstream speed can be up to 640 Kbps as a conservative with bridge taps and wire diameter greater(Pressure) will increase the speed of transmission from client to service provider.

The ADSL modem or router at the customer with a standard 2-pair telephone line for service provider DSL Access Multiplexer (DSLAM) terminates interface. At this point, the service of their DSLAMs interconnection with a variety of different devices, such as T1, T3, SONET, Frame Relay, ATM or DSL circuits for transmission over the Internet or to another office.As already mentioned, some customers for sharing the ADSL line to use their phone as well. The DSLAM is removed from the data traffic and voice traffic is routed, a Class 5 switch, which is sent over the PSTN via a protocol such as SS7. Many enterprise customers a line for additional data, the increase in costs, however, when the number is not available, has decided to no impact on their Internet connection.

Very High Rate DSL (VDSL) is greaterspeed DSL specification that will transmit data at distances between 1,000 feet and 4,500 feet across copper telephone lines. Distances of approximately 1000 feet will support speeds of 55 Mbps while distances of 4,500 feet will support an approximate speed of 12 Mbps. There are some technical differences with line encoding however the modem will split off the telephone service as does ADSL for phone calls.

Symmetric DSL (SDSL) is somewhat new and as the name suggests transmits data in both directions at T1 speeds. The distance specification from the central office is 21,000 feet and it should be noted that there must be a separate phone line since SDSL won't split off phone traffic. That is currently an issue that is being addressed and should be available this year. SDSL is an always-on service, which reduces the issues with call setup. That and the higher upstream traffic rates make it better suited for web hosting applications since your file downloads sent with downstream traffic is sent with their upstream traffic. There are tremendous opportunities for service providers to sell cost effective high speed Internet access to many clients across the United States today. Telecommuters and business clients can reduce costs with higher speed circuits for sending voice and data from home, access and distribution offices across the Internet.

SONET/SDH

The Synchronous Optical Network (SONET) specification describes a high speed fiber technology used by service providers for transporting voice and data traffic. A SONET network is built with a series of ring segments that are inter-connected. Each SONET segment is comprised of dual counter rotating rings for link diversity should one of the rings be unavailable. The standard OC-1 interface is 51.8 Mbps. The SONET network ring is built with Add/Drop Multiplexers (ADM) which terminate the SONET signal at various metropolitan and national locations. They are Time Division Multiplexers that mux/demux SONET signals from an OC-12 to OC-48 traffic stream. Each ADM has an active and a standby connection to the SONET ring. When a network failure with the active connection is detected, the standby connection is immediately activated. The SONET frame structure is 810 bytes that is comprised of overhead and payload bytes. The overhead is comprised of section and line signaling. The payload bytes are comprised of path signaling and payload. Customer routers such as the Cisco 7507 that support OC-3 interfaces that can interface with an ADM.

Dense Wave Division Multiplexing (DWDM)

Dense Wave Division Multiplexers (DWDM) are used to multiplex optical signals at various wavelengths onto a single fiber strand for transport across an optical network at speeds from OC-48 to OC-192. Each wavelength can run at speeds of up to 10 Gbps. Current optical systems can multiplex as many as 100 wavelengths or channels per fiber strand which is almost 1 Terabit (1000 Gbps) aggregate speed. Current efforts are focused on developing multi-terabit transport on 1 fiber strand. This technology is somewhat of a demarcation between the fastest enterprise core networks and the long haul ISP core networks which aggregate hundreds of enterprise customers. The enterprise customer can connect with DWDM networks using ATM switches and IP routers with OC-48 interfaces. Public and private SONET network providers have rings that connect using equipment with interfaces running at OC-48 speeds as well. The Cisco 12016 Gigabit switch router is available with OC-48 interfaces. Companies today are utilizing 400 OC-48 router interfaces at the 12016 to build a Terabit WAN core.

Data Link Switching (DLSW+)

Data Link Switching is a Layer 2 protocol used for encapsulating SNA frames across an IP WAN. It is an IP encapsulation method that integrates SNA workstations and servers with the IP enterprise network. Encapsulation of SNA is required since there is no Layer 3 addressing defined with its protocol stack. Routers that are configured with DLSW+ will establish peer relationships with local and remote DLSW+ routers. Each SNA Frame is encapsulated in an IP packet before it is sent across the WAN to a peer router configured with DLSW+. Each local router will terminate LLC2 data link layer frames from each workstation and send local acknowledgments to each local workstation as packets are sent and received. That eliminates LLC2 timeout issues that can occur between workstation and server when acknowledgments must travel across a congested WAN circuit.

SNA is connection-oriented and must receive data link acknowledgments every few seconds or the session will timeout. Bridge protocols such as Source Route Bridging (SRB) limit the number of bridges and rings that an SNA packet can span. There is no issue with the number of Rings utilized with DLSW+ since the RIF field is terminated at the router. DLSW+ integrates many different data link technologies such as Ethernet, Token Ring, SDLC and Frame Relay. There is a translation as well between different frame types such as Ethernet and Token Ring at each router for those data link technologies. Promiscuous mode is configured at DLSW+ routers which allows for many connections from remote peer routers. An example would be 7500 Data Center routers that have peer connections from many distribution offices.

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