Nortel Networks 9150 - Manual (Page 35)

Remote Gateway 9150 Installation and Administration Guide 5
January 2005 Remote Gateway 9150 description
Collisions
Half-duplex Ethernet connections only allow their nodes to either send or
receive packets at any given time. Collisions occur when two nodes on a half-
duplex Ethernet connection attempt to transmit information simultaneously.
Before transmitting, the Network Interface Card (commonly referred to as the
NIC card) monitors the line, or listens, for transmissions. A NIC card listens to
the line for the amount of time that it takes to transfer a minimum-sized packet
the maximum length of the cable. If the NIC card senses no transmission from
the destination node, it proceeds with its own transmission.
If a NIC card detects a collision, it waits for a period of time determined by the
back-off algorithm, then re-transmits the packet. Ethernet nodes keep track of
how many times they must re-transmit a packet with a maximum collision re-try
counter. In previous versions of Remote Gateway 9100 Series software, the
maximum collision re-try counter had a limit of 15. After 16 unsuccessful
attempts to transmit a packet (the original attempt plus 15 re-tries) the Remote
Gateway 9100 Series unit dropped the packet. In an effort to decrease delay and
improve QoS, the limit of the maximum collision re-try counter is now eight.
After nine unsuccessful attempts to transmit a packet (the original attempt plus
eight re-tries) the Remote Gateway 9100 Series unit drops the packet and begins
attempting to transmit the next packet.
Note: Since Ethernet traffic has a nominal speed of 10 Mbps, the flashing
Ethernet COLL, TX, RX LED indicators are cosmetic. They do not reflect real-
time traffic patterns or packets.
Connectors
The following connections are made from the rear panel of the Remote Gateway
9150 unit to the telephone and data networks:
!
Two 25-pair connectors (labeled TELCO 1 and TELCO 2) provide tip and
ring connections to user stations (telephones) and central office trunks
(ISDN BRI).
These connections provide the interface to the telephone network and the
Public Switched Telephone Network (PSTN).
!
An RJ-45 connector (labeled ETHERNET) provides a 10BaseT Ethernet
connection.
This connection provides the ability to pass both voice and data traffic over
the existing Ethernet network.