Electric Energy T&D - Index
Electric Energy T&D - EE Magazine March / April - Index
If the configuration is done as both-way
as shown in Figure 1, any of the two sides
can start the connection. The remote IP
address and remote port are necessary to be
configured for scheme to work.
Figure shows the OSI Model applied to RaW
Socket serial to Ethernet mode of operation.
figure 2 OSI Model of RaW Socket TCP/IP
RaW Socket encapsulation will permit
encapsulating serial traffic into IP packets.
During the encapsulation process a decision
will need to be made about when to packetize
serial information.
The following options are available on state
of the art serial server devices for Raw
Socket encapsulation:
figure 1 RaW Socket Operation
• packetize on receiving a specific character:
The server will examine each received
character and will packetize and forward
upon receiving the specific character.
The character is usually a
(0 to 55) character.
• packetize on timeout: The server will wait
for a configurable time after receiving a
character before packetizing and forwarding.
If another character arrives during the
waiting interval, the timer is restated. This
method allows characters transmitted as a
part of an entire message to be forwarded
to the network in a single packet, when the
timer expires after receiving the very last
character of the message.
• packetize on full packet: The server will
always packetize and forward on a full
packet, i.e. when the number of characters
fills its communications buffer (1K bytes).
figure 3 RaW Socket Packatization
Comparing Serial with Ethernet
Communications
Comparing the characteristics of Serial vs.
Ethernet communications, the following are
the most important reasons when considering
one versus the other:
70 I March-April 2008 Issue
1. Reliability of Data communication
The Ethernet is a secure and proven way of
data communication with error connection
handled by the hardware and the TCP world
standard communication protocol.
The primary limiting factor for shared-bus
topologies like serial links is that of high
I/O and limited distance.
. Speed of Data communication
Using Ethernet data is moving with a
minimum speed of 1 Mbps with absolute
error correction compared to RS 3
where the speed is at best one tenth of the
Ethernet’s minimum, without or minimum
error correction.
3. Ethernet better and faster Recovery
Ethernet networks utilize redundant links
and recovery protocols as protection
techniques against link failures.
4. Standardized cable and connection
For the Ethernet network the engineer is
using world class unshielded twisted pair
(UTP) cables and plugs however in the
serial world there are no cable standards.
5. Distance of Data communication and
Noise immunity
When using Ethernet technology the data
can be error free at high speed of 1mbps
minimum over distances up to 50m. When
using the RS 3 for speeds of 110kbps
the theoretical distance for error free
communication is relatively very short.
This means that in the majority of cases
the distance alone between the IED and
the PC is a key factor to choose Ethernet
over serial communications. Furthermore
in noisy environments the Ethernet cable
is proven to work while the RS 3 or
RS485 non standard cables offer no
guarantee that may corrupt data.
Serial to Ethernet Migration
Example
In the early 1970’s, utilities began deploying
communications to substations, in some
cases having looped source feeds for the
purpose of providing Distance Protection
Pilot Schemes such as Permissive
Overreach Transfer Trip (POTT) highspeed
relaying between the substations.