Specifications

B-2
Cisco 1800 Series Integrated Services Routers (Fixed) Software Configuration Guide
OL-6426-02
Appendix B Concepts
SHDSL
SHDSL
SHDSL is a technology based on the G.SHDSL (G.991.2) standard that allows both data and voice to be
transmitted over the same line. SHDSL is a packet-based network technology that allows high-speed
transmission over twisted-pair copper wire between a network service provider (NSP) central office and
a customer site, or on local loops created within either a building or a campus.
G.SHDSL devices can extend the reach from central offices and remote terminals to approximately
26,000
feet (7925 m), at symmetrical data rates from 72 kbps up to 2.3 Mbps. In addition, it is repeatable
at lower speeds, which means there is virtually no limit to its reach.
SHDSL technology is symmetric in that it allows equal bandwidth between an NSP central office and a
customer site. This symmetry, combined with always-on access (which eliminates call setup), makes
SHDSL ideal for LAN access.
Network Protocols
Network protocols enable the network to pass data from its source to a specific destination over LAN or
WAN links. Routing address tables are included in the network protocols to provide the best path for
moving the data through the network.
IP
The best-known Transmission Control Protocol/Internet Protocol (TCP/IP) at the internetwork layer is
IP, which provides the basic packet delivery service for all TCP/IP networks. In addition to the physical
node addresses, the IP protocol implements a system of logical host addresses called IP addresses. The
IP addresses are used by the internetwork and higher layers to identify devices and to perform
internetwork routing. The Address Resolution Protocol (ARP) enables IP to identify the physical address
that matches a given IP address.
IP is used by all protocols in the layers above and below it to deliver data, which means that all TCP/IP
data flows through IP when it is sent and received regardless of its final destination.
IP is a connectionless protocol, which means that IP does not exchange control information (called a
handshake) to establish an end-to-end connection before transmitting data. In contrast, a
connection-oriented protocol exchanges control information with the remote computer to verify that it
is ready to receive data before sending it. When the handshaking is successful, the computers have
established a connection. IP relies on protocols in other layers to establish the connection if
connection-oriented services are required.
Internet Packet Exchange (IPX) exchanges routing information using Routing Information Protocol
(RIP), a dynamic distance-vector routing protocol. RIP is described in more detail in the following
subsections.
Routing Protocol Options
Routing protocols include the following:
• Routing Information Protocol (RIP)
• Enhanced Interior Gateway Routing Protocol (Enhanced IGRP)